Comorbidity as a moderator of process -outcome relations in individual and family therapy for adolescent substance abuse

Abstract

This study investigated the effects of comorbidity on psychotherapy process and treatment outcome. The adolescent subjects participated in a randomized clinical trial (Liddle, 2002) and were assigned to one of two empirically supported treatments, Cognitive Behavioral Therapy (CBT) or Multidimensional Family Therapy (MDFT). Some studies have found that youth with multiple diagnoses have poorer treatment outcomes than adolescents with a pure substance abuse disorder (Grella et al., 2004; Rowe et al., 2004; Shane et al., 2003; Tomlinson et al., 2004). According to the Generic Model of Psychotherapy, input variables impact psychotherapy process, which in turn impact treatment outcome (Orlinsky & Howard, 1986). It was hypothesized that comorbidity would negatively impact process variables (i.e., therapeutic alliance, therapist adherence, and competence) and act as a moderator, restricting process-outcome effects. ^ Subjects were placed into one of two groups, youth with single or dual diagnoses and youth with multiple diagnoses. Mixed ANOVAs were conducted to evaluate the impact of comorbidity on process variables. Contrary to hypotheses, results indicated comorbidity did not have a negative impact on process variables. Next, hierarchical linear regressions were conducted to evaluate the moderator hypotheses. Results indicated comorbidity moderated adherence-retention relations only. In CBT, greater therapist adherence was associated with increased retention. Conversely, in MDFT, higher adherence was associated with reduced retention. In both treatments, the association between variables was stronger for youth with a single diagnosis or dual diagnoses than multiple diagnoses. The link between stages-of-change variables and premature treatment termination (Brogan et al., 1999; Prochaska & Norcross, 2001; Smith et al., 1995) was cited as one possible explanation for the negative association between adherence and retention in MDFT. In addition, this study proposed that other client factors, such as readiness to change and interpersonal factors may have more of an impact on the therapeutic process than comorbidity. The implications these results have on the Generic Model were discussed as well as the positive clinical implications of the unsupported hypotheses. Information from this study can be used to generate guidelines for therapists when working with youth with comorbid diagnoses and bring these treatments closer to dissemination into community clinics. ^